Control method for thermo-electric heating of a vehicle seat

ABSTRACT

Conditioned air discharged from a vehicle heating, ventilation and air conditioning (HVAC) unit is further conditioned by a thermoelectric (TE) air temperature control module and then directed to air passages in a vehicle seat. Activation of the TE air temperature control module is based on climate control parameters utilized by the HVAC unit, including the set temperature and the cabin air temperature.

RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/329,711, filed on Jan. 10, 2006, and assigned to the assignee of the present invention.

FIELD OF THE INVENTION

The present invention relates to thermoelectric temperature regulation of a vehicle seat, and more particularly to a method of controlling seat heating.

BACKGROUND OF THE INVENTION

Occupant comfort in a motor vehicle can be effectively addressed by controlling the temperature of the cabin air and by regulating the temperature of seating surfaces. Various mechanisms for achieving both cabin air and seat temperature control are well known in the art. See, for example, the U.S. Pat. Nos. 5,918,930 and RE38,128 in respect to seat temperature control. In U.S. Pat. No. 5,918,930, thermally conditioned air ordinarily discharged from the vehicle's heating, ventilation and air conditioning (HVAC) system is routed through passages in the vehicle seats; and in U.S. Pat. No. RE38,128, air handling modules including Peltier thermoelectric (TE) devices draw cabin air over the TE units and deliver the heated or cooled cabin air to passages in the vehicle seats. However, a more effective approach is to install a TE module in series between the HVAC system and the vehicle seat passages. This dramatically improves the transient thermal regulation of the seats, providing significantly faster cool-down when the HVAC system is in a cooling mode and significantly faster warm-up when the HVAC system is in a heating mode. In any event, the present invention is directed to a heating mode control strategy for a TE unit configured to supply conditioned air to air passages of a vehicle seat.

SUMMARY OF THE INVENTION

The present invention provides an improved method of operation for a heated vehicle seat in which a TE air temperature control module supplies conditioned air to air passages in the seat. Preferably, air discharged from the vehicle HVAC unit is further conditioned by the TE air temperature control module and then directed to the air passages in the seat. Activation of the TE air temperature control module is based on climate control parameters utilized by the HVAC unit, including the set temperature and the cabin air temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a vehicle including an HVAC system, a TE air temperature control module and a vehicle seat;

FIG. 2 is a diagram of the TE air temperature control module of FIG. 1;

FIG. 3 is a diagram of a microprocessor-based HVAC controller for carrying out the control method of the present invention;

FIG. 4 is a graph illustrating transient and steady-state regimes of the control of the present invention;

FIG. 5 is a graph depicting first and second target seat temperature schedules and an interpolated target seat temperature determined according to this invention;

FIG. 6 is a graph depicting the determined target seat temperature vs. cabin air temperature for various values of the HVAC set temperature; and

FIGS. 7A, 7B and 7C together form a flow diagram representing a software routine executed by the HVAC controller of FIG. 3 for carrying out the control of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the reference numeral 10 generally designates a motor vehicle including a cabin 20 and occupant seats 22 a and 22 b. At least one of the seats 22 a is provided with internal air passages 24, including perforated seat and back cushions. Air supplied to the seat 22 a via the air duct 26 flows through the air passages 24 to cool or heat the seating surfaces for enhanced occupant comfort. A heating, ventilation and air conditioning (HVAC) unit 28 develops conditioned air based on an operator temperature control setting, and supplies the conditioned air to cabin ducts 30 and one or more seat ducts 32. The cabin ducts 30 convey the conditioned air to cabin vents 34 and the seat duct 32 conveys the conditioned air to a thermoelectric (TE) air temperature control module 36. The TE air temperature control module 36 further conditions a portion of the air supplied to it via seat duct 32; the further conditioned air is supplied to the air passages 24 of seat 22 a by the air duct 26, and the remaining air is exhausted into the cabin 20 through the exhaust duct 38. A vehicle electrical system including a storage battery 40 supplies electrical power to the HVAC unit 28, which in turn, supplies electrical power to the TE air temperature control module 36.

Referring to FIG. 2, the TE air temperature control module 36 includes a Peltier TE device 42 and a pair of heat exchangers 44, 46. A flow divider 48 positioned in the seat duct 32 apportions the inlet air from HVAC unit 28 between the heat exchangers 44 and 46. Inlet air directed through heat exchanger 44 is supplied to the seat passages 24 via air duct 26, while air directed through heat exchanger 46 is exhausted into the cabin 20 via exhaust duct 38. A thermal insulator 52 disposed between the ducts 26 and 38 downstream of the TE device 42 inhibits the transfer of thermal energy between the ducts 26 and 38.

In operation, the HVAC unit 28 selectively activates the TE device 42 to further heat or chill the air flowing through heat exchanger 44 to provide optimal occupant comfort. In the illustrated embodiment, the control of TE device 42 is implemented by a microcontroller (uC) 28 a resident within a control head of HVAC unit 28. Referring to FIG. 3, microcontroller 28 a is responsive to a number of inputs provided by the temperature sensors 60-63, the solar sensor 64, and optionally by the relative humidity sensor 65. The temperature sensors 60 and 61 are located in the bottom and back cushions of seat 22 a, respectively, and produce the seat temperature signals designated as Tseat_bot and Tseat_bk. The temperature sensors 62 and 63 are responsive to the temperatures of ambient air and cabin air, respectively, and produce the temperature signals designated as Tamb and Tcabin. The solar sensor 64 may be a conventional automotive solar radiation sensor, or a mean radiant temperature sensor, and produces a signal designated as SOLAR. The relative humidity sensor 65 is responsive to the humidity in ambient air, and produces a signal designated as RH. An additional input designated as Tset is supplied by a vehicle occupant through a user interface device 66, and represents the occupant's set temperature—i.e., the desired cabin air temperature. The microcontroller (uC) 28 a executes a number of resident software routines for developing various HVAC-related outputs, including a duty-cycle output DC on line 72 representing the desired mode (heating or cooling) and activation level of TE air temperature control module 36. The duty-cycle output is supplied to a thermoelectric power supply (TEPS) 76 which correspondingly activates the TE device 42 of TE air temperature control module 36 using battery voltage Vb.

The present invention is directed to a control method carried out by the microcontroller 28 a during the HVAC heating mode when HVAC unit 28 supplies heated air to the cabin and seat ducts 30, 32 in order to satisfy the occupant set temperature Tset. Referring to FIG. 4, the seat temperature control carried out by microcontroller 28 a includes a transient regime during which the TE device 42 is fully activated for maximum heating of the air supplied to the seat ducts 30, 32, followed by a steady-state regime during which the activation of TE device 42 is modulated to maintain the seat temperature Tseat within 2° C. of the target seat temperature Ttar. The control transitions from the transient regime to the steady-state regime when the seat temperature Tseat enters a temperature control band defined as Ttar±2° C.

The target seat temperature Ttar is determined based on thermal comfort considerations for any combination of cabin temperature Tcabin and set temperature Tset. The fundamental constraints on Ttar are determined for a nominal set temperature Tset such as 25° C., and include a first schedule (referred to herein as Ttar_cold) for cold cabin temperatures (say, 10° C. or less) and a second schedule (referred to herein as Ttar_warm) for warm cabin temperatures (say, 35° C. or more). The schedules Ttar_cold and Ttar_warm are of the form:

Ttar_cold=(K1*Tcabin³)+(K2*Tcabin²)+(K3*Tcabin)+K4, and

Ttar_warm=(K1*Tcabin³)+(K2*Tcabin²)+(K3*Tcabin)+K5

where K1-K3 are calibrated coefficients, and K4 and K5 are calibrated offsets. By way of example, the offset K5 may be 4.4° C. less than the offset K4. For intermediate cabin temperatures, the target seat temperature Ttar is linearly interpolated between the first and second schedules. This is graphically depicted in FIG. 5, where the reference numerals 80 and 82 respectively designate the schedules Ttar_1 and Ttar_2, and the reference numeral 84 designates the determined value of Ttar. When the set temperature Tset varies from its nominal value, the determined value of Ttar is progressively adjusted at a calibrated rate such as 0.6° C. for each 1° C. of deviation from the nominal value. Since the driver can vary Tset over a wide range, Ttar is additionally capped at a calibrated limit value such as 45° C. Of course, Ttar can be determined in a multi-step process as described, or by combining the above considerations into a single calculation, or by performing a 2-D table-look up. In any event, the graph of FIG. 6 illustrates the resulting value of target seat temperature Ttar vs. cabin temperature Tcabin for five different values of set temperature Tset.

In operation, microprocessor 28 a periodically updates the target seat temperature Ttar based on Tcabin and Tset, and activates TE device 42 of TE air temperature control module 36 as generally described above in reference to FIG. 4. The flow diagrams of FIGS. 7A-7C illustrate the control algorithm as a software routine periodically executed by microcontroller 28 a during the heating mode of HVAC unit 28. When seat temperature control is first enabled in a given period of vehicle operation, the blocks 90-92 configure the TE device 42 for heating at a maximum activation level. The various inputs described above in reference to FIG. 3 are sampled at block 94, and block 98 calculates the seat temperature Tseat as the average of the seat temperature inputs Tseat_bot and Tseat_bk. The block 100 is then executed to determine the target seat temperature Ttar based on Tcabin and Tset as described above.

The block 102 determines the current mode (heating or cooling) of the TE device 42. Initially, the TE device will be configured for heating due to the operation of block 92; in this case, block 102 is answered in the affirmative, and the blocks 104-116 of FIG. 7B are executed as indicated by the flow connector B. Referring to FIG. 7B, the block 104 determines if Tseat is within 2° C. of Ttar. If so, the current activation level of TE device 42 is maintained. If Tseat is not within 2° C. of Ttar, the block 106 determines if Tseat is greater than Ttar. Thus, block 106 will be answered in the affirmative if Tseat is above Ttar by at least 2° C., and in the negative if Tseat is below Tseat by at least 2° C. When block 106 is answered in the negative (Tseat too cold), the block 108 is executed to incrementally increase the activation level of TE device 42, if it is not already at the maximum level. When 106 is answered in the negative (Tseat too warm), the blocks 110 and 112 incrementally decrease the activation level of TE device 42 if activated. If TE device 42 has already been adjusted to the minimum activation level, the block 114 changes the mode of TE device 42 to cooling. So long as seat temperature control continues to be enabled, microcontroller 28 a is returned to block 94 of FIG. 7A as indicated by the flow connector A; otherwise, the routine is exited.

If the mode of TE device 42 is changed to cooling as described above, the block 102 of FIG. 7A will direct microcontroller 28 a to execute the blocks 118-130 of FIG. 7C as indicated by the flow connector C. Referring to FIG. 7C, the block 118 determines if Tseat is within 2° C. of Tseat_tar. If so, the current activation level of TE device 42 is maintained. If Tseat is not within 2° C. of Tseat_tar, the block 120 determines if Tseat is greater than Tseat_tar. Thus, block 106 will be answered in the affirmative if Tseat is above Tseat_tar by at least 2° C., and in the negative if Tseat is below Tseat_tar by at least 2° C. When block 120 is answered in the affirmative (Tseat too warm), the block 122 is executed to incrementally increase the activation level of TE device 42, if it is not already at the maximum level. When 120 is answered in the negative (Tseat too cool), the blocks 124 and 126 incrementally decrease the activation level of TE device 42 if activated. If TE device 42 has already been adjusted to the minimum activation level, the block 128 changes the mode of TE device 42 to heating. So long as seat temperature control continues to be enabled, microcontroller 28 a is returned to block 94 of FIG. 7A as indicated by the flow connector A; otherwise, the routine is exited.

In summary, the present invention provides an easily implemented control method for supplemental thermoelectric heating of a vehicle seat. The control method accounts for changes in the cabin and set temperatures, and achieves a desired occupant comfort level without requiring extensive calibration effort. While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the disclosed control method could be used in a system where the HVAC discharge air or even cabin air is drawn through the TE air temperature control module 36 by an auxiliary fan, and so on. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims. 

1. A method of operation for a thermoelectric air temperature control module that delivers conditioned air to a passenger seat of a vehicle, where the vehicle additionally includes a heating, ventilation and air conditioning (HVAC) unit, the method comprising the steps of: measuring a temperature of air in a cabin of said vehicle; determining a target seat temperature during a heating mode of said HVAC unit based on a set temperature of said HVAC unit and the measured cabin air temperature; measuring a temperature of said seat; and controlling an operating mode and an activation level of said thermoelectric air temperature control module to bring the measured seat temperature into conformance with said target seat temperature.
 2. The method of claim 1, including the steps of: decreasing the activation level of said thermoelectric air temperature control module to provide less seat heating when the operating mode of said thermoelectric air temperature control module is heating and said measured seat temperature is above the target seat temperature by at least a calibrated value; increasing the activation level of said thermoelectric air temperature control module to provide more seat heating when the operating mode of said thermoelectric air temperature control module is heating and said measured seat temperature is below the target seat temperature by at least said calibrated value; and changing the operating mode of said thermoelectric air temperature control module from heating to cooling when said measured seat temperature is above the target seat temperature by at least said calibrated value and the activation level of said thermoelectric air temperature control module has been decreased to a minimum level.
 3. The method of claim 2, including the steps of: increasing the activation level of said thermoelectric air temperature control module to provide more seat cooling when the operating mode of said thermoelectric air temperature control module is cooling and said measured seat temperature is above the target seat temperature by at least said calibrated value; decreasing the activation level of said thermoelectric air temperature control module to provide less seat cooling when the operating mode of said thermoelectric air temperature control module is cooling and said measured seat temperature is below the target seat temperature by at least a calibrated value; and changing the operating mode of said thermoelectric air temperature control module from cooling to heating when said measured seat temperature is below the target seat temperature by at least said calibrated value and the activation level of said thermoelectric air temperature control module has been decreased to the minimum level.
 4. The method of claim 1, including the steps of: controlling said thermoelectric air temperature control module to provide maximum heating of the air delivered to said passenger seat upon initial activation of said HVAC unit in said heating mode.
 5. The method of claim 1, where the step of determining the target seat temperature includes the steps of: determining a first target seat temperature based on the measured cabin air temperature using a schedule derived for cabin temperatures greater than a calibrated upper temperature; and adjusting said first target seat temperature upward based on a deviation of the measured cabin air temperature below said calibrated upper temperature to form said target seat temperature.
 6. The method of claim 1, where the step of determining the target seat temperature includes the steps of: determining a nominal target seat temperature based on the measured cabin air temperature, using a schedule derived for a nominal value of said set temperature; and adjusting said nominal target seat temperature up or down based on a deviation of said set temperature above or below said nominal value to form said target seat temperature.
 7. The method of claim 1, including the step of: limiting the determined target seat temperature to a calibrated maximum value. 